DETROIT, Aug 8 (Reuters) - The auto industry continued itspoor performance in an influential U.S. safety group's new crashtest as half of the small cars tested did not fare well.

Six of the cars tested, most of which were 2013 models, wererated "poor" or "marginal." General Motors Co's ChevroletSonic and Cruze each received marginal scores, while Kia MotorsCorp's Soul and 2014 Forte were rated "poor" in theresults released on Thursday by the Insurance Institute forHighway Safety.

The IIHS increased the rigor of its tests last year toinclude crashes that involve only a front corner of a vehicle.The insurance group said nearly one-fourth of U.S.front-of-vehicle crashes that result in serious injury or deathinvolve only a single corner that strikes another vehicle or anobject like a tree or utility pole.

The IIHS continues to score vehicles on side, rear, rolloverand front-end crashes that impact more than just a corner.

"This is a challenging new crash test and it's notsurprising that some vehicles are earning marginal and poorratings," IIHS spokesman Russ Radar said of the small overlapfront crash test.

"This crash scenario doesn't lend itself to a Band-Aid fixso for most manufacturers the countermeasure will have to bebuilt in when there's a full redesign," he added.

STRUCTURAL CHANGES

Vehicle manufacturers in the U.S. market often design andengineer their models to score well on IIHS safety tests and usethe results in their marketing.

"It matters because in today's world cars are so competitivethat all you need is a small flaw and your competition canexploit it," Kelley Blue Book senior analyst Karl Brauer said.

Most of the 12 small cars tested were already in productionbefore the IIHS increased the rigor of its front crash test lastyear. However, Radar said IIHS alerted the companies to the workthe group was doing on small overlap research in 2009.

The specifications of the test were not finalized until thelast year, which is late in a car's development process, Brauersaid. All automakers will eventually redesign their cars to meetthe standards to pass the new crash test, he said.

In the tests, IIHS crashes a vehicle at 40 mph into a5-foot-high barrier on the driver's side that overlapsone-quarter of the vehicle's width.

Kia pointed out that the IIHS small overlap crash test goeswell beyond federal requirements and the group has recognizednumerous Kia vehicles as top safety picks. The South Koreanautomaker said it would evaluate the results carefully, but thecompany was proud of its safety record.

GM said customer safety remains its highest priority and itis committed to its cars performing well in all types ofcrashes.

"We are aggressively working to incorporate these into ourmodels, including our small cars like the Chevrolet Sonic andCruze, where technically feasible," GM spokeswoman Sharon Baselsaid in an email.

Nissan and VW said they were proud of their cars' safetyrecords in federal crash tests and other IIHS crash tests, butthey would review the small overlap test results and incorporatewhat is learned into future designs.

WORST CASES

In the worst cases with the small cars that did not scorewell, safety cages collapsed, driver airbags moved sideways andthe crash dummy's head hit the instrument panel, and sidecurtain airbags did not deploy or provide enough protection,IIHS chief research officer David Zuby said.

The small car segment was the fourth group of cars ratedusing this new test, and most of the groups have fared equallybadly.

Last summer, seven of 11 luxury sedans evaluated rated"marginal" or "poor," and 12 of 15 small SUVs tested also failedto score well in results released in May. Family sedans scoredthe best, with only five of 18 scoring "marginal" or "poor" inresults released last December.

As a group, the small cars fared worse than the mid-sizedfamily sedans, but better than the small SUVs, IIHS said.Results on the new crash test for minicars will be releasedlater this year.

The other six small cars tested included two- and four-doorversions of Honda Motor Co Ltd's Civic, which bothreceived "good" ratings. The Civic was tested earlier this yearand the results were released in March.

All the cars scoring well received "Top Safety Pick +"ratings by the insurance trade group. Vehicles earning theinstitute's "Top Safety Pick +" award have received "good"ratings in the four traditional tests plus "good" or"acceptable" ratings in the small overlap test.

IIHS said it did not test the Toyota Corolla because theautomaker plans to release a redesigned 2014 model this month.